The investigators have found that the photoactive dye methylene blue (MB) plus light (MB+L) very effectively inactivates the HIV-1 virus in cultured human peripheral blood mononuclear cells.The effective dose of MB is very low (about 24 nM) and the light required is also of low intensity for a short duration. In addition, MB has a favorable absorption spectra for use with blood components. Therefore an adaptation of this approach may be useful to inactivate the HIV virus in blood components. It is highly likely that MB+L inhibition of HIV-1 propagation is mediated by a singlet oxygen mechanism and that the lethal lesion occurs at a very specific target. In contrast to other possible photoactive approaches where the mechanism of action appears to be at the viral membrane, based on extensive mechanistic studies on MB+L killing of RNA viruses in the applicant's laboratory, the investigators think that the MB+L lethal target of the HIV-1 virus is at a RNA secondary structure area, probably at a specific essential RNA/protein interaction interface. The applicants want to conduct basic studies which will help us understand the mechanistic basis to MB+L mediated inactivation of HIV and utilize the knowledge gained to design and test strategies that will achieve improvement in viral inactivation without causing significant damage to blood components, such as platelet concentrates. The investigators propose a series of experiments designed to: Understand the site and nature of MB+L damage to HIV propagation. Applicants plan to determine whether HIV infectivity is diminished by treating isolated HIV virions with MB+L. If the virions are damaged, it will be determined if the viral RNA is damaged and ascertain the specific region (residue) where the lethal lesion occurs and determine if its formation is mediated by singlet oxygen. It will also be determined if MB+L damages viral proteins or viral envelope lipids and ascertain the mechanisms involved as well as the specificity of the damage. It will also be determined if the HIV RNA present in cells (prior to assembly) is damaged by MB+L. The investigators will also design and test a series of methylene blue based (thiazine) derivatives in an effort to improve the specificity and efficacy in eliminating the risk of HIV infections. Finally the investigators plan to develop a procedure to apply the knowledge obtained in the above basic studies that will further eliminate the risk of HIV infection in the presence of blood components without significantly damaging the blood components.